The PIN diode is a microwave semiconductor diode which can be used as an electrically variable resistor. It can be incorporated in waveguide, coaxial, and stripline components for microwave switching, attenuation, limiting, modulation, and phase shifting. PIN diode switches have been constructed by mounting diodes in series, shunt, or a combination of the two. Historically, hybrid Si PIN diodes have been used in microwave circuits. However, to meet requirement specifications (such as insertion loss), the Si PIN diodes used are extremely small, making them difficult to bond into circuits. The parasitic bond wire inductances used to connect the diodes into the circuit reduce the bandwidth over which the device maintains an acceptable small-signal match. A monolithic device can decrease both the size of the circuit and the parasitic bond wire inductance, however, this has been difficult to achieve in Si.